Integrated circuit manufacturing technology utilizes positive photoresist type materials for photolithographically delineating patterns on substrates which later on in the process are etched by wet or dry etching techniques and are either left permanently or removed. The positive photoresist materials are spun on or are applied with different methods onto substrates. Then, the substrates are exposed using various types of radiation such as visible and/or ultraviolet light or an electron beam. Different types of exposure machines can be used to accomplish this exposure. After exposure, the substrates go through a wet or dry development process where, due to selective dissolution of certain areas, an image pattern is generated.
The remaining resist material is further exposed to dry or wet etching. This process is essential to define the pattern and to leave behind dielectric or metallic film to be utilized later on in the process sequence. Prior to this etching process the photoresist material may be treated with a blanket of deep ultraviolet radiation at a relatively high temperature. This treatment improves the resist selectivity and provides better etching and dimensional controls.
Prior to photolithographic processing, substrates are coated with different types of dielectrics and with metal films. These coated materials are of different combinations and types. The metal films are often made of very sensitive, i.e., easily chemically attacked, alloys. The nature of the thin film alloys depends upon the deposition system used, the composition of the films, deposition temperature, deposition time, and the like. Such sensitive metal films can react with other chemicals with which they come into contact. The nature of the reactions depend primarily upon the chemical formulations of the solutions utilized. One solution which can attack such sensitive metal films is the positive resist stripper which is used in stripping or cleaning of substrates after wet or dry etching of the sensitive metal films has been used to delineate metal lines or other patterns on the substrate. It is necessary in such a full lithographic process that the photoresist material, following pattern delineation, be evenly and completely removed from all exposed and unexposed areas so as to permit further operations. Even the partial remains of a resist coating in an area to be processed is undesirable as the left over residue of the photoresist material can have a detrimental effect on the yield of acceptable integrated circuits.
In the past, resist materials have been removed by one or more of the following: halogenated hydrocarbons, such as methylene chloride, amines and their derivatives, such as dimethylsulfoxide, dimethylformamide, N-methyl-2-pyrrolidinone, glycol ethers, such as ethylene glycol monomethyl ether, ethanol, ketones, such as methylethyl ketone and acetone and materials, such as isopropyl alcohol, sulfuric acid, ammonium persulfate and mixtures of caustic and phenol derivatives, as well as various other materials.
There are several drawbacks with the use of the aforementioned photoresist material removing compositions. One of the major disadvantages with the above-mentioned methods of stripping photoresist is that the materials used attack underlying metal films or lines, or they leave behind traces of photoresist films. The attack on metal films and lines appears as some form of corrosion. The corrosion of the metal may not be visible immediately after resist stripping but can appear after several days to several months, especially when the semiconductor chip fails in the field. The other symptoms of this metal attack phenomena appear in the form that the metal surface can show cosmetic pitting whereby the surface looks peppery. Sometimes the metal surface is attacked near the grain surface and microscopic craters are etched into the metal. In other cases, the metal lines are attacked thereby reducing those lines from 5% to 50% in width. It is very important to maintain the size of these lines for good circuit reliability and for the functionality of the microchips. When these lines are attacked by strippers of different types and are corroded, their size is reduced and such corrosion can cause electrical failure of the semiconductor chips. Therefore, it is very important that strippers be made of chemicals which do not attack or corrode metal films.
The present invention is directed to overcoming one or more of the problems as set forth above.